1. Field of the Invention
The present invention relates to a radiation imaging panel suitable for application to a radiation imaging apparatus using an X-ray and the like, and specifically to a method for manufacturing a photoconductive layer constituting the radiation imaging panel.
2. Description of the Related Art
Heretofore, in medical X-ray imaging, an X-ray imaging panel has been known, which uses a photoconductive layer sensitive to an X-ray as a photosensitive member for the purpose of reducing a dose of radiation exposed to a subject, improving diagnostic performance, and so on, reads an electrostatic latent image formed on the photoconductive layer by the X-ray by means of light or a large number of electrodes, and records the image thus read. A method using the X-ray imaging panel is superior in that resolution thereof is higher than fluorography by a television camera tube, which is a well-known imaging method.
The above-described X-ray imaging panel is constituted to generate charges corresponding to X-ray energy by irradiating a charge generation layer provided therein with the X-ray, and to read the generated charges as electric signals. The above-described photoconductive layer acts as the charge generation layer. Heretofore, amorphous selenium has been used for the photoconductive layer. However, X-ray absorptivity of the amorphous selenium is low in general. Accordingly, it is necessary that thickness of the photoconductive layer be formed thick (for example, 500 μm or more).
However, charge collection efficiency of the photoconductive layer decreases when such film thickness thereof is thickened. Accordingly, it is necessary to apply high voltage to the photoconductive layer. However, in this case, there is a problem that charges caused by dark current are prone to occur, which thereby decrease a contrast in a low-dose range and cause device deterioration. Moreover, there is a problem that noise (structure noise) resulting from variations in the thickness direction of the selenium is prone to be picked up. Furthermore, the photoconductive layer is usually formed by an evaporation method, and accordingly, it takes a considerable time to grow the photoconductive layer until the photoconductive layer reaches the thickness as described above, and a management for such a growing process is also cumbersome. These factors eventually lead to an increase of manufacturing cost of the photoconductive layer, which bring about an increase of cost of the X-ray imaging panel.
Considering the problems as described above, other materials of the photoconductive layer than the selenium are studied. For example, in Japanese Unexamined Patent Publication Nos. 11(1999)-237478 and 2000-249769, as a material constituting the photoconductive layer, a bismuth oxide-series complex oxides represented by a composition formula BixMOy (where M is at least one of Ge, Si and Ti, x is the number satisfying a condition 10≦x≦14, and y represents the stoichiometric atomic number of oxygen according to M and x which are described above) is described. In accordance with the bismuth oxide-series complex oxides, it can be expected that charge conversion efficiency of the X-ray is improved.
Incidentally, in the above-described Japanese Unexamined Patent Publication Nos. 11(1999)-237478 and 2000-249769, the following is described as a method for forming the photoconductive layer. Specifically, sol or gel obtained by performing hydrolysis for alkoxides of bismuth and the metal is subjected to a sintering treatment, and the sol or gel thus sintered is dispersed and coated.
However, in general, there are limitations on a filling factor of a photoconductive substance of the photoconductive layer which can be formed by the coating. Accordingly, in the photoconductive layer formed by the coating as described above, an effect of inhibiting a movement of the generated charges by a binder is large, and electric noise is increased. Therefore, there is a problem that image granularity is deteriorated.